The field of the invention relates generally to processing composite materials, and more particularly to processing composite materials utilizing a vacuum bag and an air bladder.
Composite materials are increasingly being used for the manufacture of a variety of products because of their high strength and durability along with the ability to be formed into a variety of shapes. A longstanding problem for the processing of composite materials is that they are most commonly processed using a vacuum bag. Decades ago this was thought to be an ideal solution because one process (vacuum) would provide two desired effects on the laminated preform, to pull air and volatiles from the laminate while also providing ambient pressure to consolidate the laminate. Augmentation of pressure by autoclave is used routinely for smaller components but is not practical for large parts, for example, boat hulls and wind turbine blades. Resin systems have been developed that enable the curing of pre-impregnated materials without the use of autoclaves specifically to solve the large part problem (boats and wind turbine blades). A single vacuum bag is typically used for curing these systems; however, the resulting void content in the composite is usually too high which can negatively effect strength and other properties of the composite. The single vacuum bag technique is not considered the most ideal way to make very low void content composite components without the use of an autoclave. The pressure that is applied to the preform inside the vacuum bag actually hinders the removal of bubbles by trapping the bubbles containing air and/or volatiles between the tacky layers of fiber and resin.
One known way to overcome this problem is to use multiple vacuum bags to obviate the need for a large expensive vacuum chamber. U.S. Pat. No. 7,413,694 B2 describes a vacuum bag within a vacuum bag to form an inner and outer chamber. The respective pressures in the inner and outer chambers are regulated to facilitate resin infusion into a dry fibrous preform. The level of independence achievable by this method is limited and not sufficient for pre-impregnated forms of composites. Another patent, U.S. Pat. No. 7,186,367, also describes a double vacuum bag approach. In this approach, the outer bag is constrained by an added rigid component, positioned between the inner and outer vacuum bags, from applying any pressure to the preform while the preform is under a vacuum.